Directional couplers are passive components used in the field of high frequency engineering for splitting, decoupling or coupling electromagnetic waves. Several directional couplers can be used to form a combiner which is also called cascaded power combiner as its several directional couplers are usually combined in a cascaded manner.
One kind of power directional coupler comprises two hollow conductors which are also called wave guides, hollow wave guides, rectangular wave guides, HF-wave guides, hollow-metallic wave guides, etc. Hereinafter, the term hollow conductor is used for such an item. The hollow conductors are typically brazed or welded together along two side walls facing each other. These side walls are perforated in order to provide a coupling portion for the electromagnetic waves. The coupling portion has many holes and/or slits wherein the number of holes and/or slits increases dramatically when a tight coupling shall be achieved with the power directional coupler, for instance a 3 dB coupling. At frequencies higher than 10 GHz such a power directional coupler can be operated with powers up to 400 W or more in contrast to coaxial or printed (PCB) couplers which can only be operated with low power.
In general, the size and the position of the holes and/or slits result from a complex function which further complicates the manufacturing of the power directional coupler significantly. This also applies for the manufacturing of a combiner comprising several power directional couplers.
Further, the combiner needs a lot of space due to the many holes and/or slits of each power directional coupler when 3 dB power directional couplers are used.